1. The Field of the Invention
The present invention relates generally to a spring, which are particularly useful in pneumatic instruments, such as valve controllers. More particularly, the present invention relates to springs that can be fabricated, or compressed, into a single plane, but have motion out of that plan, and one-piece, compliant springs with a platform that does not have substantial rotation throughout its deflection.
2. The Background Art
An ortho-planar spring can be defined as a spring which can be either fabricated in or compressed down into a single plane, with motion out of that plane. Prior art that fit this definition are the Belleville or disc spring 2 (FIG. 1a), the volute (conical) spring 4 (FIG. 1b), and the spider (geophone) spring 6 (FIG. 1c). These types of springs are used in bolt assemblies, disc brake assemblies, valves, pneumatic controllers, and many other applications. A major advantage of these types of springs over traditional linear springs is that they are very compact and, in many cases, they can be easily manufactured.
The disc spring 2 (FIG. 1a) is manufactured in a slightly out-of-plane position and provides resistance as it is forced down towards the plane. The volute spring 4 (FIG. 1b) is a thin strip of steel wound so that the coils fit inside of each other. It also provides resistance as it is forced down towards the plane. The spider spring 6 (FIG. 1c) is usually manufactured in the plane and provides resistance as it is forced in either direction out of this plane of fabrication. (More discussion on currently existing springs is available in common sources such as Wahl, 1963, Juvinell, 1983, and Parmley, 1985.)
One of the disadvantages of the prior art, like the spider and volute springs, is that they require some rotation to occur during their operation. One disadvantage of rotation is that anything fixed to the surface of the platform will be required to rotate with the platform. Second, if the platform is not fixed to the adjacent part, then the two components are left to slide against each other, causing wear to both parts as well as vibration and noise. The abrasion also causes particle generation which can be a problem in many environments, such as in pneumatic positioners with small nozzels, or cleanrooms used for microelectronics fabrication. Another problem with rotation is that if the platform shape is not circular, a rotating platform may require more clearance in order to avoid contact with nearby structures. This requires that a larger surface area be available to accommodate the spring that needs to obtain a given deflection. One final disadvantage is that rotation in the spider spring legs adds torsional stresses to the members.
The disc springs, like the Belleville, require clearance for either the outer or inner edges of the spring to slide. The assembly tolerances are also required to be quite tight, increasing the cost of the assembly.
One application of such springs is in pneumatic instrumentation. In pneumatic controls, a nozzle and a baffle are used to get a feedback pressure of 3–15 psi, as well as output pressures of the same magnitude. A regulated pressure of 20 psi is supplied to an instrument, and it is routed through the nozzle. As the baffle rests up against the nozzle, it causes a back pressure. The nozzle is spring loaded to give it the force. The back pressure of 0–20 psi is then used to measure, transmit, or control a process. In the case of measuring, the feedback signal of 3–15 psi can be equal to any parameter being measured. For example, in the case of temperature, 3–15 psi can be equal to 0–100 degrees. In the case of transmitting, the 3–15 psi can be run over long distant lines to read the same 0–100 degrees in a control room some distance away from the actual process. In the case of control, the 3–15 psi can be used to regulate a control valve, pneumatic cylinder, or the like. In all of these cases, the nozzle and baffle serve the same function; i.e. to get a feedback pressure of 3–15 psi. The feedback pressure may be used for different application, but the basic construction and designs are the same. Current nozzle and baffle technology has adequate resolution, but may be improved. One disadvantage is that baffles are typically positioned at an angle, causing potential hysteresis and repeatability problems.
Therefore, it would be advantageous to develop an ortho-planar spring capable of providing linear motion without significant rotation. It would also be advantageous to develop such a spring for use in pneumatic instrumentation.